Essential amino acids - Biochemistry……….

Important topic

1. Essential amino acids Kushagra Batra FMHS, SGT University Reg No. - 220101005

2. Nutritional Classification Non-essential Semi-essential Essential Leucine Isoleucine Valine Threonine Lysine Methionine Phenylalanine Tryptophan Histidine Arginine Alanine Asparagine Aspartame Cysteine Glutamine Glutamate Glycine Proline Serine Tyrosine Conditionally essential Arginine Glycine Cysteine Tyrosine Proline Glutamine Taurine

3. Essential amino acids Many amino acids are synthesised by pathways that are present only in plants and microorganisms. Hence, mammals must obtain these amino acids in their diet & are referred to as essential amino acids. The best sources of essential amino acids are animal proteins such as meat, eggs, and poultry. However, some plant foods, such as the soy products edamame and tofu, contain all the essential amino acids. This means they are “complete” sources of protein During states of inadequate intake of essential amino acids such as vomiting or low appetite, clinical symptoms may appear. These symptoms may include depression, anxiety, insomnia, fatigue, weakness, growth stunting in the young, etc.

4. Biosynthesis Essential amino acids, like nonessential amino acids, are synthesized from familiar metabolic precursors. Their synthetic pathways are present only in microorganisms and plants, however, and usually involve more steps than non essential amino acids. The enzymes that synthesise essential amino acids were apparently lost early in animal evolution possibly because of the ready availability of amino acids in the diet.

5. Biosynthesis Biosynthesis of aspartate family of amino acids Aspartate ATP ADP Aspartokinase Lysine NAD⁺ + Pi NADH β-aspartate semialdehyde dehydrogenase 8 reactions Homoserine 2 reactions Threonine 3 reactions Homocysteine Methionine N⁵-methyl THF THF Homoserine dehydrogenase Aspartyl-β-phosphate β-aspartate semialdehyde

6. Biosynthesis Biosynthesis of pyruvate family of amino acids Pyruvate TPP + Pyruvate α-ketobutyrate α-Acetolactate α-ketoisovalerate Valine Glutamate α-ketoglutarate Valine aminotransferase Hydroxyethyl-TPP α-aceto-α-hydroxybutyrate α-keto-β-methylvalerate Isoleucine Glutamate α-ketoglutarate Valine aminotransferase 3 reactions 3 reactions α-ketoisocaproate Leucine 3 reactions Glutamate α-ketoglutarate Leucine aminotransferase

7. Biosynthesis Biosynthesis of aromatic amino acids from glucose derivatives Phosphoenol pyruvate + Erythrose-4-phosphate 2-keto-3-ketodeoxyarabinoheptulosonate-7-phosphate Pi Chorismate Anthranilate Glutamine Glutamate + pyruvate Anthranilate synthase Indole-3-glycerol phosphate 3 reactions Indole Tryptophan Prephenate Tyrosine Phenylalanine Chorismate mutase Tryptophan synthase (α) Tryptophan synthase (β) Glyceraldehyde-3-phosphate

8. Catabolism The pathways of amino acid catabolism, taken together, normally account for only 10% to 15% of the human body’s energy production; these pathways are not nearly as active as glycolysis and fatty acid oxidation The 20 catabolic pathways converge to form 6 major products, all of which enter the TCA cycle From here, the carbon skeletons are diverted to gluconeogenesis or ketogenesis and are completely oxidised to CO₂ & H₂O

9. Catabolism Leucine Lysine Phenylalanine Tryptophan Acetoacetyl-CoA Acetyl-CoA Leucine Isoleucine Threonine Tryptophan Ketone bodies Citrate Isocitrate α-ketoglutarate Succinyl-CoA Oxaloacetate Fumarate Pyruvate Threonine Tryptophan Phenylalanine Isoleucine Threonine Valine Methionine - Glucogenic - Ketogenic TCA Cycle

10. Catabolism Catabolism Ketogenic amino acids The seven amino acids that are degraded entirely or in part to acetoacetyl-CoA and/or acetyl-CoA—phenylalanine, tyrosine, isoleucine, leucine, tryptophan, threonine, and lysine—can yield ketone bodies in the liver where acetoacetyl-CoA is converted to acetoacetate and then to acetone and hydroxybutyrate Their ability to form ketone bodies is particularly evident in uncontrolled diabetes mellitus, in which the liver produces large amounts of ketone bodies from both fatty acids and the ketogenic amino acids.

11. Glucogenic amino acids The amino acids that are degraded to pyruvate, α-ketoglutarate, succinyl CoA, fumarate, and/or oxaloacetate can be converted to glucose and glycogen Catabolism The division between ketogenic and glucogenic amino acids is not sharp. Both ketogenic and glucogenic tryptophan, phenylalanine, threonine, and isoleucine Exclusively ketogenic Leucine - very common in proteins. Its degradation makes a substantial contribution to ketosis under starvation conditions. Lysine Exclusively glucogenic Methionine

12. Uses Phenylalanine Our body turns this into neurotransmitters tyrosine, dopamine, epinephrine & norepinephrine. It plays an integral role in the structure and function of proteins and enzymes and the production of other amino acids Threonine This is a principal part of structural proteins, such as collagen and elastin, which are important components of your skin and connective tissue. It also plays a role in fat metabolism and immune function Methionine It plays an important role in metabolism and detoxification. It’s also necessary for tissue growth and the absorption of zinc and selenium, minerals that are vital to your health

13. Uses Leucine Like valine, leucine is a BCAA that is critical for protein synthesis and muscle repair. It also helps regulate blood sugar levels, stimulates wound healing, and produces growth hormones Valine This is one of three branched-chain amino acids (BCAAs). That means it has a chain branching off from one side of its molecular structure. It helps stimulate muscle growth and regeneration and is involved in energy production Isoleucine The last of the three BCAAs, isoleucine is involved in muscle metabolism and is heavily concentrated in muscle tissue. It’s also important for immune function, hemoglobin production, and energy regulation

14. Lysine plays major roles in protein synthesis, calcium absorption, and the production of hormones and enzymes. It’s also important for energy production, immune function, and the production of collagen and elastin Uses Tryptophan Often associated with drowsiness, tryptophan is a precursor to serotonin, a neurotransmitter that regulates your appetite, sleep, and mood

15. Disorders Medical condition Approx incidence (per 100,000 births) Defective process Defective enzyme Symptoms & effects Homocystinuria <0.5 Methionine degradation Cystathionine-β-synthase Faulty bone development, mental retardation Maple syrup urine disease (branched chain ketoaciduria) <0.4 Isoleucine, leucine & valine degradation Branched chain keto acid dehydrogenase complex Vomiting, convulsions, mental retardation, early death Phenylketonuria <8 Conversion of phenylalanine to tyrosine Phenylalanine hydroxylase Neonatal vomiting,
Mental retardation

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